Knife project tool is looking rough after I extrude on a curved surface
Apply an Edge Split modifier to your object and then select the loop edges one for each letter-symbol (if I count correctly there should be 5) and then once you select them press Spacebar and search mark sharp and press Enter

Then in your Edge Split modifier select only Sharp Edges.

However this will only fix the solution 90%. If you zoom in really close to the area with the letters you will see some "unwanted" shading. In that case I would suggest to delete the letters and try what comments suggest.